You would do this exactly the same way as you would extract/export to WAV format.
Once you've isolated the sample you wish to use in FL Studio (you can either have it as a selection or in a separate Audacity project), go to File ---> Export to MP3. Name your sample and save it in one of your FL-recognised directories, refresh your FL Studio browser (if you've got it running - I normally do) and you're good to go!
I actually personally prefer to export my samples to WAV rather than MP3. Never actually looked into what the difference is - as far as I'm aware FL Studio supports both file formats throughout it's interface.
Last edited by Nifty1Pound50; 04-18-2007 at 09:03 AM..